This invention relates generally to magnetic disk data storage systems, and more particularly to the use of piezoelectric materials to damp vibrations within the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system of the prior art includes a sealed enclosure 12, a spindle motor 14, a magnetic medium or disk 16, supported for rotation by a drive spindle Si of the spindle motor 14, a voice-coil actuator 18 and an arm 20 attached to an actuator spindle S2 of voice-coil actuator 18. A read/write head support system consists of a suspension 22 coupled at one end to the arm 20, and at its other end to a read/write head 24.
The read/write head 24 typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the read/write head 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16.
Discrete units of magnetic data, known as "bits," are typically arranged sequentially in multiple concentric rings, or "tracks," on the surface of the magnetic medium. Data can be written to and/or read from essentially any portion of the magnetic disk 16 as the voice-coil actuator 18 causes the read/write head 24 to pivot in a short arc, as indicated by the arrows P, over the surface of the spinning magnetic disk 16. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
Fundamentally, magnetic disk drives are electro-mechanical devices incorporating rapidly moving or spinning components. The different motions within a drive may induce various components to vibrate. Vibrations can be deleterious to the performance of a disk drive and may increase data retrieval times, reduce accuracy, reduce total storage capacity, and lead to possible catastrophic failure. Therefore, controlling and minimizing vibrations have become critical to the magnetic disk drive industry.
FIG. 2 is a perspective view of a Voice-Coil Motor (VCM) 30 and Head Stack Assembly (HSA) 40 showing commonly used viscoelastic dampers according to the prior art. The VCM consists, in part, of two substantially parallel magnetic plates 32 and 32'. A prior art viscoelastic VCM damper 34 is usually attached to the exterior surface of magnetic plate 32.
The Head Stack Assembly 40 consists, in part, of an actuator arm, 20, a suspension 22, and a read/write head 24. A prior art viscoelastic actuator arm damper 44 is normally attached to the actuator arm 20, and a prior art viscoelastic suspension damper 46 is attached to the suspension 22. Together, the VCM 30 and the HSA 40 control the positioning of the read/write head 24 relative to the magnetic storage medium. The disk drive control logic directs the movement of the read/write head 24 through a preamplifier 38 and a flexible cable 42. A prior art viscoelastic flexible cable damper 48 is attached to the flexible cable 42.
One of the key areas for vibration control in a disk drive 10 is the suspension 22 that holds the read/write head 24 out over the surface of the rapidly spinning magnetic disk 16. One possible vibrational mode for the suspension 22 is a bending mode in which the suspension 22 flexes up and down bringing the read/write head 24 alternately closer and further away from the magnetic disk 16. Such a vibration is undesirable for at least three reasons. Firstly, as the read/write head 24 moves further away from the surface of the magnetic disk 16, its ability to read the magnetic information on the magnetic disk 16 diminishes rapidly. Secondly, as the read/write head 24 moves closer to the magnetic disk 16 the likelihood of the read/write head 24 inadvertently touching the surface of the magnetic disk 16 increases. Contact between the read/write head 24 and the magnetic disk 16 can create wear debris, and in some instances even lead to a catastrophic failure of the device frequently referred to as "head crash." As designers build drives with ever lower "fly heights," preventing unwanted contact between the read/write head 24 and the magnetic disk 16 becomes increasingly difficult and controlling vibrations becomes increasingly important. Thirdly, vibration of the suspension 22 causes modulation in the signal being read from or written to the magnetic disk 16 by the read/write head 24.
Other vibrational modes of the suspension 22 can include torsional modes and side-to-side bending, sometimes referred to as sway. These vibrational modes can also create modulations in the signal being read from or written to the magnetic disk 16. Side-to-side bending of the suspension 22 while writing to the magnetic disk 16 may also cause broadening of the trackwidth. Broadening the trackwidth may cause adjacent tracks to overlap, resulting in a loss of data. However, allowing extra space between tracks decreases the number of tracks that can be written on the surface of the magnetic disk 16 and therefore reduces its total storage capacity. Therefore, reducing vibrations could allow tracks to be placed closer together, leading to higher storage capacities.
Another problem associated with vibrations of the suspension 22 is the time it takes for the read/write head 24 to stabilize its position over a particular track after being moved between tracks, sometimes referred to as settling time. Delays in stabilization over a desired track may increase the delay before data can be accessed or written. In other words, damping the vibrations of suspension 22 will improve its dynamic characteristics, thereby enhancing disk drive overall access time.
Vibrations in other components connected to the suspension 22 also may contribute to unwanted vibrations in the suspension 22. Therefore, it may be desirable to damp the vibrations of components such an actuator arm 20, a Voice-Coil Motor (VCM) 30, and a flexible cable 42. Damping the vibrations of components, generally may be desirable for several additional reasons. Vibrations in a mechanical device may reduce the device's overall longevity by loosening connectors, seals, and filters, and creating excessive wear in moving parts. Vibrations can also lead to frayed wires, metal fatigue, and particle generation.
Vibration control in disk drives has commonly been achieved through the use of passive damping. In the prior art, passive damping has been accomplished by attaching constraining viscoelastic materials to components that are known to vibrate. Viscoelastic materials damp vibrations by creating passive resistance to bending and twisting motions. There are drawbacks, however, to the use of viscoelastic vibration dampers. One problem is that viscoelastic materials are frequently polymeric and tend to degrade as they age, loosing their damping effectiveness while outgassing and shedding particles. Outgassing and particle contamination may pollute the surface of the magnetic disk 16 and lead to problems such as "head crash" or the inability of the read/write head 24 to lift off of the surface of the magnetic disk 16 and "fly." Additionally, viscoelastic materials typically loose damping efficiency with increasing temperature. Since the temperature within the disk drive 10 typically increases as it operates, vibrations of components within the disk drive 10 may worsen as the drive is used.
Accordingly, what is desired is a damping system for more efficiently reducing vibrations of components of data storage and retrieval systems. Also, a damping system is desired that can maintain its damping efficiency over a longer period of time, and over a greater range of temperatures, with less particle generation and outgassing than may be found in the prior art. A damping system is further desired that can be tunable to provide damping only to vibrations within a selected range of frequencies.